This invention relates to intrinsic conductive polymers. In particular to the patterning of layers of such polymers in order to form electrodes on said layers.
It is known in the art of fabrication of flexible LC displays, electroluminescent devices and so on to replace the transparent ITO (Indium-Tinoxide) electrodes by transparent electrodes made with intrinsically conductive polymers as e.g. polyacetylene, polypyrrole, polyaniline, polythiophene, etc. The advantage of this replacement resides mainly in the fact that electrodes made with conductive polymers are much more flexible and less brittle than ITO electrodes so that, especially in the manufacture of touch screens, where high flexible electrodes are needed, the lifetime of the device can be prolonged.
Different methods for forming tracks of electrodes made from intrinsic conductive polymers have been disclosed. In WO-A-97 18944 a continuous layer of a conductive polymer is applied to the substrate, a mask is applied on top of said layer and the no masked parts are etched. After washing the mask away a pattern of electrodes is produced. In U.S. Pat. No. 5,561,030 basically the same procedure is used to form the pattern except for the fact that the pattern is formed in a continuous layer of prepolymer which is not yet conductive and that after washing the mask away the remaining prepolymer is rendered conductive by oxidation.
In U.S. Pat. No. 4,699,804 it is disclosed to apply a pattern of a polymerization catalyst to a substrate and on that pattern a polymerizable compound. After reaction between the polymerization catalyst and the polymerizable compound a pattern of conductive polymer is formed.
All methods above use some kind of lithography and etching processes as known from the classical PCB production and require a plurality of steps to be performed. There is thus a need to have a simple process, requiring a low number of steps, to prepare substrate with an electrode pattern.
It is an object of the invention to provide a method for producing tracks of electrodes on a substrate wherein said electrodes are made of intrinsically conducting polymers requiring only a few number of process steps.
It is a further object of the invention to provide a method for producing tracks of electrodes on a substrate, said electrodes being made of intrinsically conducting polymers, wherein said tracks are formed by digital printing means.
Further objects and advantages of the invention will become clear from the description herein after.
The objects of the invention are realized by providing a method for producing a pattern of electrodes in a conductive polymer on a substrate comprising the steps of
applying a layer containing between 10 and 5000 mg/m2 of a conductive polymer on a substrate so as to prepare a conductive layer and
printing an pattern on said layer using a printing solution containing of an oxidant selected from the group consisting of ClOxe2x88x92, BrOxe2x88x92, MnO4xe2x88x92, Cr2O7xe2x88x92xe2x88x92, S2O8xe2x88x92xe2x88x92 and H2O2 
It was found that an electrode pattern on a substrate wherein the electrodes are formed by a conductive polymer could be produced by applying a conductive layer on the substrate and then printing a pattern on said layer using a printing solution containing an oxidant. It was found that by printing a solution containing an oxidant the conductivity of the polymeric layer could be changed (diminished) by a factor between 103 and 1011 without changing the thickness of the layer. This is advantageous, especially when the electrode pattern is used in displays as, e.g., LCD""s, since it makes it possible to use fewer spacing particles.
It is preferred to use an oxidant selected from the group consisting of ClOxe2x88x92, BrOxe2x88x92, MnO4xe2x88x92, Cr2O7xe2x88x92xe2x88x92, S2O8xe2x88x92xe2x88x92 and H2O2. It is highly preferred to use ClOxe2x88x92 or MnO4xe2x88x92 as oxidant. The use of MnO4xe2x88x92 has the advantage that the influence on the conductivity of the conductive polymer is in a pH-range from 3 to 10 almost independent of the pH of the printing solution containing the MnO4xe2x88x92 ions, so that no problems with aging of the printing solution are encountered. The use of ClOxe2x88x92 as oxidant has the advantage that the printing solution can be used in low concentration or that, with printing solution containing a fairly high concentration, a small amount of printing solution can be used, thus avoiding problems with drying and spreading of the solution, which makes it possible to print lines as narrow as 5 xcexcm. Therefore the use of ClOxe2x88x92 is most preferred.
The printing can proceed by offset printing, screen-printing or ink-jet printing.
Using a printing solution with a low concentration of ClOxe2x88x92 as oxidant makes it possible to prepare an ink that has a sufficient oxidizing strength to change the conductivity of the conductive layer, but that is not so corrosive that it would be unusable in ink jet printing devices. The use of ink-jet printing devices has the advantage that no screens are necessary and that the electrode layout can be printed directly from the computer on the conductive layer.
For adjusting the viscosity of the solutions, a thickener is added selected from the group consisting of silica, silicates, clay, synthetic clays, e.g. the clays sold under trade name LAPONITE, and polymeric thickeners.
Optionally for easy printing the printing solution may comprise surfactants.
Although the printing works with layers containing any intrinsically conductive polymer known in the art, e.g., polyacetylene, polypyrrole, polyaniline, polythiophene, etc., it is preferred to use layers prepared by applying a mixture containing
(a) a polythiophene with formula 
wherein each of R1 and R2 independently represents hydrogen or a C1-4 alkyl group or together represent an optionally substituted C1-4 alkylene group or a cycloalkylene group, preferably an ethylene group, an optionally alkyl-substituted methylene group, an optionally C1-12 alkyl- or phenyl-substituted 1,2-ethylene group, a 1,3-propylene group or a 1,2-cyclohexylene group,
(b) a polyanion compound and
(c) an organic compound containing 2 or more OH and/or COOH groups or amide or lactam groups. Such layers have been described in EP-A-686 662.
The printing can proceed on layers containing of a polyethylene-di-oxythiophene, polystyrenesulphonic acid wherein between 10 and 5000 mg/m2 of the polythiophene is present, preferably layers wherein between 50 and 1000 mg/m2 of the polythiophene is present are used and more preferably layers wherein between 75 and 500 mg/m2 of the polythiophene is present are used. The layers comprising a conductive polymer and printed in the method of this invention can have any conductivity. The method of this invention can, e.g., be used to pattern layers with conductivity between 1 and 105 S/cm. Preferably the conductive layers patterned by the method of this invention have conductivity between 5 and 104 S/cm, more preferably between 10 and 1000 S/cm.